Forced cooling in steam turbine plants

ABSTRACT

A turbine plant ( 3 ), in particular a steam turbine plant, and a method ( 100 ) for cooling the turbine plant ( 3 ). The turbine plant ( 3 ) has a turbine ( 29 ) through which a process gas ( 15 ) flows in a flow direction ( 27 ) during operation. A cooling medium ( 7 ) is drawn or blown ( 120 ) through the turbine ( 29 ) either in or counter to the process gas flow direction ( 27 ) respectively, cooling the turbine ( 29 ). A fan ( 6 ) may be coupled to either a turbine inlet ( 4 ) or to a turbine outlet ( 5 ). The fan acts on the cooling medium ( 7, 110 ) which is drawn into the turbine ( 29 ) through the turbine inlet ( 4 ) or through the turbine outlet ( 5 ) to be blown ( 120 ) through the turbine ( 29 ) in or counter to the process gas flow direction ( 27 ).

The invention relates to a turbine plant, in particular a steam turbineplant, and to a method for cooling a turbine plant, in particular asteam turbine plant.

Steam power stations, otherwise known as thermal power stations, areextensively known, for example from

-   http://de.wikipedia.org/wiki/Dampfkraftwerk (retrieved 4/24/2012).

A steam power station is a type of power station for generatingelectricity from fossil fuels, in which thermal energy from steam isconverted into kinetic energy in a steam turbine—generally a multi-partsteam turbine—

-   (http://de.wikipedia.org/wiki/Dampfturbine, retrieved 4/24/2012) and    is further converted into electrical energy in a generator.

In the case of such a steam power station, a fuel, for example coal, isburned in a burner space, releasing heat.

The heat released in this manner is taken up by a water-tube boiler, inshort a steam generator, where it converts previously purified andprepared (feed) water, fed into the boiler, into steam/high-pressuresteam. Further heating the steam/high-pressure steam in a superheaterincreases the temperature and specific volume of the steam.

The high-pressure steam generated moves further—via an inflow side, i.e.what is referred to as a fresh steam side, FD side for short, or asupply line (FD supply line) located there—into a high-pressure sectionof the steam turbine (high-pressure turbine section) where it performsmechanical work as it expands and cools.

In order to achieve a high overall efficiency, once the steam has leftthe high-pressure section—via the waste steam side thereof or a wastesteam discharge line located there—it is returned to the steam generatorand undergoes intermediate superheating.

The (intermediate-)superheated steam is again supplied—via an inflowside, i.e. what is referred to here as a hot intermediate superheaterside, HZU side for short, or a supply line (HZU supply line) locatedthere—to an intermediate-pressure section of the steam turbine(intermediate-pressure turbine section) where it performs moremechanical work as it further expands and cools.

After leaving the intermediate-pressure section via the waste steam sidethereof, or a waste steam discharge line located there, the steam flowsvia an overflow line into a low-pressure section of the steam turbine(low-pressure turbine section), where it performs more mechanical workas it expands and cools to waste steam pressure.

The generator coupled to the steam turbine then converts the mechanicalpower into electrical power, which is supplied to a grid in the form ofelectrical current.

The waste steam from the steam turbine, or from the low-pressure turbinesection, flows via the waste steam side thereof, or a waste steamdischarge line located there, into a condenser where it condenses bytransfer of heat to the surroundings and collects as liquid water.

Via a condensate pump and through a preheater, the water is held in afeed water container and is then once again supplied to the boiler bymeans of a feed pump, thus closing a (water-steam) circuit of the steampower station.

A distinction is drawn between various types of steam power station,such as coal-fired power stations, oil-fired power stations, or alsogas-and-steam combined-cycle power stations (COGAS power stations),according to their different methods for generating steam or the fuelused for generating steam.

A coal-fired power station is for example a special form of steam powerstation, in which coal is used as the predominant fuel for generatingsteam. Such coal-fired power stations are known for lignite and for hardcoal.

In addition to steam power stations, gas power stations, or gas turbinepower stations, are also known

-   (http://de.wikipedia.org/wiki/Gasturbinenkraftwerk, retrieved    4/24/2012).

Such a gas turbine power station is a power station which is operatedusing petroleum products or combustible gases such as natural gas. Thesegases are in this case the fuel for a gas turbine(http://de.wikipedia.org/wiki/Gasturbine, retrieved 4/24/2012) which inturn drives the generator coupled thereto.

A COGAS power station is described in

-   http://de.wikipedia.org/wiki/Gas-und-Dampf-Kombikraftwerk (retrieved    4/24/2012).

A COGAS power station of this type is a power station in which theprinciples of the gas power station and of the steam power station arecombined. The gas turbine serves here as a heat source for a downstreamwaste heat boiler which in turn serves as a steam generator for thesteam turbine.

Work such as maintenance or overhaul work on a turbine of a powerstation, such as on a steam turbine of a steam power station, can becarried out only after rotational operation of the turbine has beenswitched off. To that end, it is necessary for a shafting of the turbineto be cooled from temperatures in the region of 600° C. to below 100° C.

The steam turbine cools for example—without external intervention—inroughly 8 days, or approximately 200 hours, to below 100° C., or inroughly 6 days, or approximately 150 hours, to below 150° C. This lattermoment is the earliest point at which the shafting, or the shaft of thesteam turbine, can be shut down, although this must then be furtherrotated manually in order to avoid thermally-induced deformations ofrotating parts of the shafting, which would hamper rotational operation.

Although gas turbines cool down faster than steam turbines, on accountof having less material than steam turbines, cooling-down times withoutexternal intervention are long here too.

In order to reduce the time necessary for overhaul work, it is desirableto minimize the cooling-down times of a turbine, such as a steam turbinebut also of a gas turbine or the turbine sections thereof, while keepingto permissible cooling rates.

In order to minimize these still considerable cooling-down times, inparticular in the case of steam turbines, it is known to use thereinwhat is termed forced cooling (Forced Cooling of Steam Turbines,Performance Enhancement—Steam Turbine, Answers for energy. Siemens A G,2009).

In a steam turbine, this forced cooling involves drawing or blowingambient air—instead of the (high-pressure) steam—as a coolant throughthe steam turbine, or through the turbine sections thereof, in theoperational flow direction of the turbine.

The condenser downstream of the steam turbine is used in the context ofthe forced cooling as the pressure sink which initiates the suction flowthrough the steam turbine, wherein a vacuum with respect to the ambientair is generated inside the condenser (evacuation of the condenser) bymeans of vacuum pumps, for example using elmo pumps.

In order to ensure that as many as possible of the hot steam turbinecomponents are cooled, the ambient air must be able to act on all thesteam-guiding components of the steam turbine.

To that end, the ambient air—aspirated via the vacuum prevailing in theevacuated condenser—is allowed to flow in via (air) pipes betweenquick-closing valves and control valves, in each case on the FD side andHZU side or via the FD supply line or HZU supply line located there,whereby the coolant—then aspirated by the vacuum in the condenser—flowsthrough the steam turbine or the turbine sections thereof in theoperational flow direction of the steam.

The cooling effect of the ambient air cools the steam turbine—or thecomponents thereof—and thus achieves faster cooling of the steam turbinecomponents.

Since permissible cooling gradients for the steam turbine components maynot be exceeded, which could otherwise lead to damage to components, thequantity of ambient air aspirated by means of the pressure sink in theevacuated condenser must be regulated. To that end, the control valvesin the supply lines serve as regulating members.

A disadvantage of the known forced cooling technique is the necessarypresence of the condenser for generating the pressure sink, or thesuction flow of the coolant.

In the meantime, however, numerous steam turbine plants having steamturbines without a low-pressure turbine section and then also without acondenser have been created, with the steam turbines working inback-pressure operation. In the case of such back-pressure steam turbineplants without a condenser, for example in back-pressure steam powerstations for seawater desalination plants, the known forced coolingcannot be used or there are no known other solutions for forced cooling.

The invention is based on the object of overcoming the disadvantages andlimitations of the prior art in the context of maintenance or overhaulof a power station or of a turbine, in particular of a steam powerstation or of a steam turbine, more particularly of a back-pressuresteam power station or of a back-pressure steam turbine plant without acondenser.

The invention is also based on the object of overcoming disadvantagesand limitations of the prior art in the context of cooling of the powerstation or of the turbine, in particular of a back-pressure steam powerstation or of a back-pressure steam turbine plant without a condenser,in particular in the event of switching off the rotational operation ofthe turbine.

The object is achieved with a turbine plant, in particular a steamturbine plant, and with the method for cooling a turbine plant, inparticular a steam turbine plant, having the features as claimed in therelevant independent claim.

The turbine plant relevant to the invention has a turbine through whicha process gas can be made to flow in a flow direction from a turbineinlet to a turbine outlet when the turbine plant is in operation.

It is provided, according to the invention, that a fan is coupled to theturbine inlet or to the turbine outlet of the turbine.

Using this fan, which is provided according to the invention and iscoupled to the turbine, a coolant sucked into the turbine via theturbine inlet by means of the fan coupled to the turbine outlet can beblown through the turbine in the operational process gas flow direction,or a coolant sucked into the turbine via the turbine outlet by means ofthe fan coupled to the turbine inlet can be blown through the turbinecounter to the operational process gas flow direction.

According to the method for cooling a turbine plant having a turbinethrough which a process gas can be made to flow in a flow direction froma turbine inlet to a turbine outlet during operation, a coolant is drawninto the turbine by means of a fan coupled to the turbine inlet or tothe turbine outlet, and is drawn through the turbine in or counter tothe operational process gas flow direction, whereby the turbine iscooled by the coolant.

In other words, or more simply, the invention creates, in the case of aturbine and by means of a fan coupled to the turbine inlet or to theturbine outlet, a pressure sink at the turbine inlet or at the turbineoutlet.

The pressure sink initiates a suction flow in or counter to the processgas flow direction through the turbine, by means of which a coolant,aspirated at the respective other end of the turbine depending on thecoupling side of the fan, is drawn through the turbine in or counter tothe process gas flow direction. The turbine is cooled by the coolantdrawn through the turbine.

The invention thus proves to be most advantageous in many respects.

The coolant drawn through the turbine—in or counter to the process gasflow direction—by the suction flow acts on all of the steam guidingcomponents of the turbine and thus ensures that all of the hotcomponents of the turbine are cooled. This achieves efficient, effectiveand rapid cooling of the turbine.

The invention thus makes it possible to minimize the cooling-down timesof a turbine such as a steam turbine but also a gas turbine, or of theirturbine sections. Overhaul times or downtime of turbines or turbineplants can thus be reduced, resulting in financial savings.

In particular, the invention makes it possible—using the fan accordingto the invention to create a pressure sink at the turbine inlet oroutlet—to effect forced cooling also in turbines or turbine plantswithout a condenser or without a low-pressure turbine section andwithout a condenser.

It is thus possible by means of the invention to use forced cooling alsoin known back-pressure steam turbine plants which work without acondenser or without a low-pressure turbine section and without acondenser, such that these plants can also be cooled faster and overhaultimes and downtime there can be reduced.

Preferred developments of the invention will also emerge from thedependent claims. The described developments relate both to the turbineplant and to the method for cooling a turbine plant.

According to one preferred development, the fan is coupled to theturbine outlet, in particular to a waste steam duct at the turbineoutlet. In this context, the coolant then drawn into the turbine via theturbine inlet can be sucked through the turbine in the operationalprocess gas flow direction. In particular, coupling the fan to the wastesteam duct is simple to carry out in terms of construction.

A further preferred development provides that the fan is coupled to theturbine inlet, in particular to a fresh steam/HZU/overflow supply lineat the turbine inlet. For example, the fan may be connected to an airpipe located there.

In this case, then, the coolant drawn into the turbine via the turbineoutlet can be sucked through the turbine counter to the operationalprocess gas flow direction.

A suction flow of the coolant through the turbine counter to theoperational process gas flow direction proves to be of particularadvantage since the coolant enters the turbine at the “cold” side. Thisproduces, in the turbine components, cooling gradients which are smallerand load the component less than in the case of the coolant entering atthe “hot” side of the turbine.

Furthermore, in the case of multi-part turbines, which then generallyhave one (or in each case a plurality of) high-pressure turbinesection(s) and intermediate-pressure turbine section(s) and/orlow-pressure turbine section(s), it can also be provided that the fan iscoupled to the high-pressure turbine section, the intermediate-pressureturbine section and/or the low-pressure turbine section of the turbine.Multiple fans may also be provided for multiple such turbine sections.

Thus, here, it may also be further provided that, depending on how thepressure sink is created (by the fan) at a waste steam side (turbineoutlet) or a supply or fresh steam side (turbine inlet) of such aturbine section, the fan is coupled to a waste steam duct or to a freshsteam/HZU/overflow supply line of the high-pressure turbine section, ofthe intermediate-pressure turbine section and/or of the low-pressureturbine section.

A further preferred development provides that the coolant is ambientair. This is easily available and is available in sufficient quantitiesand at usable temperatures.

The coolant, in particular the ambient air, can then flow into theturbine or turbine section via a pipe connected to the turbine, forexample an air pipe on the fresh steam side or HZU side of the turbineor turbine section.

It is particularly preferred if the flow of the coolant into the turbinecan be controlled, regulated and/or governed by means of a valve. Thus,i.e. by regulating a quantity of coolant entering the turbine or turbinesection, it is possible to ensure that permissible cooling gradients arenot exceeded. A control valve can be used as a regulating member.

In this context, i.e. for regulating the quantity of coolant, the valve,for example the control valve or regulating valve, can be arranged atany point in the coolant path, for example also at the fan inlet.

According to a particularly preferred development, the coolant flowsinto the turbine or turbine section via an air pipe arranged betweenvalves, for example between a quick-closing valve and a control valve,on the fresh steam side or HZU side of the turbine or turbine section.The quantity of inflowing coolant can be controlled, regulated and/orgoverned via the control valve so as to not exceed permissible coolinggradients for the turbine components.

According to another preferred development, the process gas is steam.I.e. the turbine is a steam turbine or, respectively, the plant is asteam turbine plant.

Furthermore, in this case the turbine or steam turbine can be amulti-part turbine or steam turbine. This can have one or more turbinesections, such as high-pressure turbine sections, intermediate-pressureturbine sections and/or low-pressure turbine sections.

Particularly preferably, the turbine plant is a steam turbine plantwithout a condenser, for example a back-pressure steam turbine plantwithout a low-pressure turbine section and without a condenser. Theinvention provides in this case, by means of the fan used according tothe invention, a pressure sink which is otherwise not present, wherebyforced cooling is possible also in the case of such a steam turbineplant without a condenser. It is now possible, by means of theinvention, to shorten downtime also in the case of such a steam turbineplant without a condenser.

Forced cooling according to the invention—by means of the pressure sinkproduced by the fan and the coolant flow thus initiated through theturbine or turbine section—can be effected separately for one or in eachcase multiple turbine sections, by in each case multiple separatecoolant throughflows and correspondingly multiple fans, or also jointlyfor multiple successive turbine sections, in the case of a commoncoolant throughflow, by means of a single fan.

In one further preferred development, thermal protection or overheatingprotection is provided for the fan.

A fan as used according to the invention is limited in terms of itsoutlet temperature, i.e. the temperature of the medium blown out by thefan, for example to 150° C. Accordingly, therefore, the inlettemperature of the medium sucked in by the fan is also limited, forexample to 120° C. if the medium flowing through the fan is assumed tobe heated by 30° C.

In order to provide the thermal protection for the fan, it can beprovided that a further coolant supply, for example a bypass or bypasspipe, is attached at or in the region of the inlet of the fan, via whichbypass or bypass pipe a further coolant, for example also ambient air,can be admixed with the coolant leaving the turbine and drawn into thefan. A temperature sensor may also be arranged at the fan outlet, bymeans of which the temperature of the medium leaving the fan ismeasured.

If this bypass is furthermore also provided with a control valve, thefurther coolant can be admixed in a manner that can be controlled,governed and/or regulated with the coolant leaving the turbine and drawninto the fan, in particular taking into account the measured fan outlettemperature, and thus overheating of the fan can be prevented.

It is also possible to control, govern and/or regulate the admixingand/or the quantity of the further coolant by means of a three-way mixerat the point of bringing together the further coolant and the coolantleaving the turbine and drawn into the fan.

It is also possible to control, regulate and/or govern the admixing ofthe further coolant using a turbine temperature, and/or the temperatureof the coolant aspirated by the fan and/or the temperature of theadmixed further coolant.

At the start of the forced cooling, only a small quantity of coolant fedthrough the turbine is necessary in order to achieve the maximumpermissible cooling rate or in order to achieve the permissible coolinggradients of the turbine components. The turbine, which at that momentis still at a high temperature, causes this small quantity of coolant—byexchange of heat with the very hot turbine components—also to be heatedto a high temperature.

In order to cool the coolant—which at that moment is therefore veryhot—flowing out of the turbine and to bring it to an inlet or outlettemperature which is permissible for the fan, the further coolant, forexample also ambient air, is admixed via the bypass.

As the turbine temperature drops, the quantity of coolant through theturbine is increased, and at the same time the admixed further coolantquantity is reduced.

It is thus possible to effectively prevent the fan from overheatingwhile at the same time “utilizing the maximum cooling rates of theturbine components”.

The medium leaving the fan, i.e. the fan exhaust air, may be dischargedto the surroundings—with the shortest possible flow path so as to avoidpressure losses. It is thus also possible to avoid heating a machineroom incorporating the turbine.

Furthermore, it can also be provided that steam-precooling of theprocess gas, for example steam injection cooling of the process gas, iscarried out before the forced cooling according to the invention.

The above description of advantageous refinements of the inventioncontains numerous features which are reproduced in the individualsubclaims, in some cases combined into groups. However, a person skilledin the art will expediently also consider these features individuallyand combine them into appropriate further combinations.

The figures show exemplary embodiments of the invention which will beexplained in more detail below. Identical reference signs in the figuresdenote technically identical elements.

In the figures:

FIG. 1 shows a section of a water-steam circuit in a steam power stationhaving a steam turbine plant for forced cooling according to oneexemplary embodiment of the invention,

FIG. 2 shows a section of a water-steam circuit in a steam power stationhaving a steam turbine plant for forced cooling according to a furtherexemplary embodiment of the invention,

FIG. 3 is a conceptual representation of thermal protection for a fan ofa steam turbine plant for forced cooling according to one exemplaryembodiment of the invention,

FIG. 4 is a representation of mass flow rates of a coolant through theturbine and of a further coolant through a bypass in the case of forcedcooling in a steam turbine plant according to one exemplary embodimentof the invention,

FIG. 5 is a representation of forced cooling or cooling of a turbine ina steam turbine plant according to one exemplary embodiment of theinvention.

Exemplary embodiments: forced cooling in steam turbine plants withoutcondensers or in steam power stations having steam turbine plantswithout condensers (FIGS. 1 to 5).

FIG. 1 shows a section of a water-steam circuit 2 in a steam powerstation 1 having a steam turbine plant 3 without a condenser.

When the steam power station 1 is in operation, hot steam/high-pressuresteam 15, which has been heated by a steam generator and further heatedby a superheater and which in the following is denoted only as processgas 15, flows via a supply line 30 into the steam turbine 29 via aturbine inlet 4 on a fresh steam side 13 of said steam turbine 29, andflows through the steam turbine 29, in the process gas flow direction27, where it performs mechanical work as it expands and cools.

A generator (not shown) coupled to the steam turbine 29 then convertsthe mechanical power into electrical power, which is supplied to a gridin the form of electrical current.

The expanded process gas 15 leaves the steam turbine 29 via a turbineoutlet 5—in the form of a waste steam pipe 9—located on the waste steamside 31 of the steam turbine 29, and flows via a waste steam line 9 backto the steam generator, thus closing the water-steam circuit 2.

The flow of process gas 15 into or, respectively, away from the steamturbine 29 is controlled or governed by means of valves 12, 11 arrangedin the supply line, i.e. a quick-closing valve 12 and a regulating valve11, and by means of a butterfly valve 33 arranged in the waste steamline 9.

Work on the steam turbine 29, such as maintenance or overhaul work, canbe carried out only after rotational operation of the steam turbine 29has been switched off. To that end, it is necessary for a shafting (notshown) of the steam turbine 29 to be cooled from operating temperaturesin the region of 600° C. to below 100° C.

Without external intervention, this cooling would take several days,specifically approximately 8 days, and would extend the overall downtimeof the steam power station 1 by that time.

In order to reduce this downtime, or to shorten the cooling-down phase,forced cooling is used in the steam turbine plant 3 or in the steamturbine 29.

In this forced cooling (FIG. 5, 100) in the steam turbine 29, instead ofthe process gas 15, ambient air 7 is sucked (FIG. 5, 110) into the steamturbine from the surroundings 14 as a coolant 7, and the ambient air 7is drawn or blown (FIG. 5, 120) through the steam turbine 29 in theoperational process gas flow direction 27 (in this case also the coolantflow direction 28), so as to ensure cooling (FIG. 5, 130) of as many aspossible of the hot steam turbine components.

In order to generate a necessary vacuum (pressure sink) which initiatesthe suction flow of the coolant 7 in the steam turbine 29 or in theoperational process gas flow direction 27 (in this case also the coolantflow direction 28) through the steam turbine 29, a fan 6 is connected,as shown in FIG. 1, to a suction line (which is open during forcedcooling) on the steam turbine waste steam side 31, between the turbineoutlet 5 and a butterfly valve 33 (which is closed during forcedcooling).

The coolant 7 or the ambient air 7 then enters the steam turbine 29 viaan air pipe 10 between the quick-closing valve 12 (which is closedduring forced cooling) and the regulating valve 11 (which is partiallyopen during forced cooling) on the fresh steam side 13 of the steamturbine 29.

The cooling effect of the ambient air 7, as it flows through the steamturbine 29 in the coolant flow direction 28 (in this case also theoperational process gas flow direction 27), cools the steam turbine29—or, specifically, the components thereof —and thus achieves fastercooling of the steam turbine components.

The ambient air 7, aspirated, by the fan 6, through the steam turbine 29in the operational process gas flow direction 27 or the coolant flowdirection 28, is again released into the surroundings 14 as fan exhaustair 20.

Since permissible cooling gradients in the steam turbine components maythen not be exceeded, which could otherwise lead to damage to thecomponents, the quantity of the aspirated ambient air 7 is regulated. Tothat end, the regulating valve 11 at the turbine inlet 4 (on the freshsteam side 13) serves as regulating member.

FIG. 2 also shows a section of a water-steam circuit 2 in a steam powerstation 1 having a steam turbine plant 3 without a condenser.

Here too, when the steam power station 1 is in operation, hotsteam/high-pressure steam 15, or process gas 15, which has been heatedby a steam generator and further heated by a superheater, flows via asupply line 30 into the steam turbine 29 via a turbine inlet 4 on afresh steam side 13 of said steam turbine 29, and flows through thesteam turbine 29, in the process gas flow direction 27, where itperforms mechanical work as it expands and cools.

The expanded process gas 15 leaves the steam turbine 29 via a turbineoutlet 5—in the form of a waste steam pipe 9—located on the waste steamside 31 of the steam turbine 29, and flows via a waste steam line 9 backto the steam generator, thus closing the water-steam circuit 2.

Here too, the flow of process gas 15 into or, respectively, away fromthe steam turbine 29 is controlled or governed by means of valves 12, 11arranged in the supply line, i.e. a quick-closing valve 12 and aregulating valve 11, and by means of a butterfly valve 33 arranged inthe waste steam line 9.

In order to reduce here too the downtime, or to shorten the cooling-downphase, forced cooling is used in the steam turbine plant 3 or in thesteam turbine 29.

In this forced cooling (FIG. 5, 100), in the steam turbine 29, insteadof the process gas 15, ambient air 7 is sucked (FIG. 5, 110) into thesteam turbine from the surroundings 14 as a coolant 7, and the ambientair 7 is drawn or blown (FIG. 5, 120) through the steam turbine 29counter to the operational process gas flow direction 27 in the coolantflow direction 28, also so as to ensure cooling (FIG. 5, 130) of as manyas possible of the hot steam turbine components.

In order to generate a necessary vacuum (pressure sink) which initiatesthe suction flow of the coolant 7 in the steam turbine 29 or counter tothe operational process gas flow direction 27 or the coolant flowdirection 28 through the steam turbine 29, a fan 6 is in this caseconnected, as shown in FIG. 2, on the steam turbine fresh steam side 13to an air pipe 10 between the quick-closing valve 12 (which is closedduring forced cooling) and the regulating valve 11 (which is open duringforced cooling).

The coolant 7 or the ambient air 7—from the surroundings 14—then entersthe steam turbine 29 via a suction line 34 (which is open during forcedcooling) which has a regulating valve 35 (which is partially open duringforced cooling) and is located between the turbine outlet 5 and aquick-closing valve 33 (which is closed during forced cooling).

The cooling effect of the ambient air 7, as it flows through the steamturbine 29 in the coolant flow direction 28 or counter to theoperational process gas flow direction 27, cools the steam turbine29—or, specifically, the components thereof —and thus achieves fastercooling of the steam turbine components.

The ambient air 7, aspirated, by the fan 6, through the steam turbine 29counter to the operational process gas flow direction 27 or in thecoolant flow direction 28, is again released into the surroundings 14 asfan exhaust air 20.

Since, here too, permissible cooling gradients in the steam turbinecomponents may not be exceeded, which could otherwise lead to damage tothe components, the quantity of the aspirated ambient air 7 isregulated. To that end, the regulating valve 35 in the suction line 34at the turbine outlet 5 (on the waste steam side 31) serves asregulating member.

Alternatively, regulation may be effected by means of the regulatingvalve 11 on the steam turbine fresh steam side 13, thus dispensing withthe regulating valve 35 in the suction line 34.

Further in this regard, i.e. for regulating the aspirated ambient air 7during forced cooling as shown in FIG. 2, and also during forced coolingas shown in FIG. 1, the ambient air 7 can be regulated also by means ofa separate regulating valve arranged at the fan inlet 16 in the suctionline 34 (in FIG. 1) or in the line 30 (in FIG. 2). In this case, then,when the ambient air 7 is regulated by means of the separate regulatingvalve, the regulating valve 11 (in FIG. 1) or the regulating valve 35(in FIG. 2) is always open.

FIG. 3 shows a conceptual representation of thermal protection for thefan 6 of the steam turbine plant 3 as shown in FIG. 1 or FIG. 2.

The fan 6 is limited in terms of the temperature of its fan exhaust air20, for example to 150° C. Accordingly, therefore, the (fan) inlettemperature of the medium 36 sucked in by the fan 6 is also limited, forexample to 120° C. if the medium flowing through the fan is assumed tobe heated by 30° C.

In order not to exceed this maximum permissible fan exhaust airtemperature or fan inlet temperature, in the context of the thermalprotection, the supply line 30 of the fan 6 is provided, in the regionof the fan inlet 16, with a bypass 17, i.e. a further coolant supply 17.

Further ambient air 8—as further coolant 8—is aspirated via this bypass17, by means of the fan 6 and in a manner that can be regulated in termsof quantity by means of a regulating valve 18 arranged in the bypass 17,via a supply line 30 from the surroundings 14, and is admixed 140 withthe ambient air 7, for the purpose of cooling the latter, which leavesthe steam turbine 29 in the coolant flow direction 28 via the turbineoutlet 5 (cf. FIG. 1) or the turbine inlet 4 (cf. FIG. 2).

Alternatively, the quantity of further coolant 8 and the mixing oradmixing 140 of the further coolant 8 and/or with the ambient air 7 mayalso be regulated by means of a three-way mixer at the point of bringingtogether the further coolant 8 and the ambient air 7.

This ambient air mixture 36 is drawn into the fan 6 via the fan inlet 16and leaves the fan 6—as fan exhaust air 20—via a discharge line 30 onthe exhaust air side 37 thereof, into the surroundings 14.

The temperature of the fan exhaust air 20 is measured by means of atemperature sensor 19 which is arranged in the region of the dischargeline 30 for the fan exhaust air 20.

A governing unit 22 regulates, as a function of the measured fan exhaustair temperature, the regulating valve 17 and a fan motor 21 which drivesthe fan 6.

FIG. 4 shows, in a coordinate representation (abscissa 23 [Time t],ordinate 24 [mass flow rates ms]), the profile of the mass flow rates ms25, 26 of the ambient air 7 through the steam turbine 29 and of theadmixed ambient air 8 through the bypass 17 during forced cooling forthe thermal protection of the fan 6.

At the start of the forced cooling, only a small, minimal quantity of(cool) ambient air 7 fed through the steam turbine 29 is necessary orpermissible, in order to reach the maximum permissible cooling rate orthe permissible cooling gradients of the turbine components.

The steam turbine 29, which at that moment is still at a hightemperature, causes this small quantity of ambient air 7—by exchange ofheat with the very hot turbine components—also to be heated to a hightemperature.

In order to cool the ambient air 7 flowing out of the steam turbine29—which air is at that moment therefore very hot—to the fan exhaust airtemperature which is permissible for the fan 6, a maximum quantity ofthe further ambient air 8 is admixed via the bypass 17, and regulated bythe regulating valve 18.

As the steam turbine temperature drops over time t, the quantity ofambient air 7 through the steam turbine 29 is continuously increased(cf. FIG. 4, line 26), and at the same time the quantity of admixedfurther ambient air 8 is continuously reduced (cf. FIG. 4, line 25),until at the end of the forced cooling the quantity of admixed furtherambient air 8 is reduced to its minimum quantity and, respectively, thequantity of ambient air 7 through the steam turbine 29 is increased toits maximum quantity.

The mixture 36—of ambient air 7 through the steam turbine 29 and ofambient air 8 through the bypass 17—thus has, at all times during theforced cooling, a permissible fan inlet temperature when entering thefan 6 and, accordingly, a respective permissible fan exhaust airtemperature.

It is thus possible to effectively prevent the fan 6 from overheatingwhile at the same time “utilizing the maximum cooling rates of theturbine components”.

Although the invention has been illustrated and described in more detailby means of the preferred exemplary embodiment, the invention is notlimited by the disclosed example and other variations may be derivedherefrom by one skilled in the art, without departing from the scope ofprotection of the invention.

1. A turbine plant comprising: a turbine having a turbine inlet and aturbine outlet, the turbine is configured for causing a process gas toflow through the turbine in a flow direction from the turbine inlet tothe turbine outlet during operation of the turbine; a fan coupled to theturbine outlet and configured and operable to suck a coolant, which isdrawn into the turbine by the fan and via the turbine inlet, is drawnthrough the turbine in the process gas flow direction; and a bypassconnected to a further coolant supply and arranged at an inlet of thefan from the bypass and the bypass is configured to supply a furthercoolant to be admixed with the coolant leaving the turbine and theadmixed coolant being drawn into the fan.
 2. The turbine plant asclaimed in claim 1, wherein the fan is coupled to the turbine outlet, awaste steam duct at the turbine outlet, wherein the fan is configuredand operable to draw the coolant into the turbine via the turbine inletand to suck the coolant through the turbine in the operational processgas flow direction.
 3. The turbine plant as claimed in claim 15, whereinthe fan is coupled to the turbine inlet, a fresh steam/HZU/overflowsupply line at the turbine inlet, wherein the fan is configured andoperable to draw the coolant into the turbine via the turbine outlet andto suck the coolant through the turbine counter to the operationalprocess gas flow direction.
 4. The turbine plant as claimed in claim 1,further comprising: a high-pressure turbine section, anintermediate-pressure turbine section and/or a low-pressure turbinesection to which the fan is coupled and the fan is coupled to a wastesteam duct or to a fresh steam/HZU/overflow supply line of thehigh-pressure turbine section, of the intermediate-pressure turbinesection and/or of the low-pressure turbine section.
 5. The turbine plantas claimed in claim 1, wherein the coolant is ambient air; and the fanis coupled to a valve configured for controlling, regulating and/orgoverning the flow of ambient air into the turbine.
 6. The turbine plantas claimed in claim 1, wherein the process gas is steam.
 7. The turbineplant as claimed in claim 1, further comprising the turbine has an airpipe, the air pipe is disposed between two valves; the air pipe isgenerally at the turbine inlet, the pipe is configured and connected toreceive and conduct the coolant, the valves being configured to governcoolant flow through the air pipe by acting on at least one of thevalves, and the fan being configured and operable to cause coolant,controlled, regulated and/or governed by operation of at least one ofthe valves to be sucked into and through the turbine by means of the fangoverned by operation of the at least one of the valves.
 8. The turbineplant as claimed in claim 1, wherein the turbine is a multi-part steamturbine without a low-pressure turbine section, or is a turbine sectionof a a multi-part steam turbine without a low-pressure turbine section.9. A method for cooling a turbine plant having a turbine with a turbineinlet and a turbine outlet; the method comprising: flowing a process gasin a flow direction from the turbine inlet to the turbine outlet duringoperation of the turbine; stopping operation of the turbine; for coolingthe turbine after operation has stopped: drawing a coolant into theturbine by operating a fan coupled to the turbine inlet for drawing thecoolant through the turbine in the process gas flow direction duringoperation of the turbine, whereby the turbine is cooled by the coolantdrawn into the turbine.
 10. The method for cooling a turbine plant asclaimed in claim 9, further comprising drawing the coolant into theturbine via an air pipe, which is arranged in a supply line of theturbine between two valves, wherein the supply line is on a fresh steamside (FD side) of a high-pressure turbine section of the turbine, andfurther comprising before the coolant that is drawn into the fan entersthe fan, admixing a further coolant, with the coolant.
 11. The methodfor cooling a turbine plant as claimed in claim 10, wherein one of thevalves is a quick-closing valve and the other is a control valve; themethod further comprising using at least one of the valves to control,regulate and/or govern aspiration of the coolant into the turbine. 12.The method for cooling a turbine plant as claimed in claim 10, furthercomprising admixing the further coolant in a controlled, regulatedand/or governed manner, using a control valve so that the admixing isdependent on a turbine temperature and/or on the temperature of thecoolant aspirated by the fan and/or on the temperature of the admixedfurther coolant and/or on the temperature of the coolant and furthercoolant mixture expelled by the fan.
 13. The method for cooling aturbine plant as claimed in claim 1, employed in a turbine plant withouta condenser, in particular in a back-pressure turbine plant.
 14. Themethod for cooling a turbine plant as claimed in claim 10, wherein thefurther coolant comprises ambient air.
 15. A turbine plant comprising: aturbine having a turbine inlet and a turbine outlet, the turbine isconfigured for causing a process gas to flow through the turbine in aflow direction from the turbine inlet to the turbine outlet duringoperation of the turbine; a fan coupled to the turbine inlet andconfigured and operable to suck a coolant, which is drawn into theturbine by the fan and via the turbine outlet, and is drawn through theturbine counter to the process gas flow direction; and a bypassconnected to a further coolant supply and arranged at an inlet of thefan from the bypass and the bypass is configured to supply a furthercoolant to be admixed with the coolant leaving the turbine and theadmixed coolant being drawn into the fan.
 16. A method for cooling aturbine plant having a turbine with a turbine inlet and a turbineoutlet; the method comprising: flowing a process gas in a flow directionfrom the turbine inlet to the turbine outlet during operation of theturbine; stopping operation of the turbine; for cooling the turbineafter operation has stopped: drawing a coolant into the turbine byoperating a fan coupled to the turbine outlet for drawing the coolantthrough the turbine counter to the process gas flow direction duringoperation of the turbine, whereby the turbine is cooled by the coolantdrawn into the turbine.
 17. The method for cooling a turbine plant asclaimed in claim 9, further comprising drawing the coolant into theturbine via an air pipe, which is arranged in a supply line of theturbine between two valves, wherein the supply line is in a supply lineof a hot intermediate superheater side (HZU side) of anintermediate-pressure turbine section of the turbine and furthercomprising before the coolant that is drawn into the fan enters the fan,admixing a further coolant, with the coolant.